Beat the butter until smooth. Add the condensed milk and beat until smooth. Add the vanilla, milk, baking powder, pinch of salt, and flour little by little. It should form a smooth paste. Then add the nuts.
Spread a generous tablespoon of the paste on the tamal leaf. Add cajeta and a bit more of the mixture on top. Close the sides by folding them. Finally, fold the tip down and tie with a corn husk strip.
Insert the Instant Pot® rack. Add 1½ cups of water and add the tamales.
Close and lock the Instant Pot® lid. Make sure the steam release handle is turned to Sealing. Press Steam and set time to 20 Minutes.